Method of vertical deviation disc detection

ABSTRACT

A method is provided to detect whether vertical deviation occurs as an optical disc spins in an optical disc player having a pickup head pre-installed in a balanced position at a focal distance. When moving towards and away from the balanced position, the pickup head generates a focus error signal with an S-curve. According to an input control signal, a focus actuator actuates the pickup head to keep it substantially at the focal distance. When the pickup head is not focused, the waveform of the input control signal is designed to actuate the pickup head back and forth within a predetermined range to generate the focus error signal with S-curves. Zero crossing points of S-curves are identified and input control values in the input control signal are obtained accordingly. The variation of the input control values is calculated, and whether vertical deviation occurs is determined by a predetermined procedure.

RELATED APPLICATIONS

This is a continuation application of U.S. application Ser. No.10/867,692, filed on Jun. 16, 2004, which in turn claims priority toTaiwanese Application 092118777, filed on Jul. 9, 2003, all of which areincorporated by reference herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a detection method, and moreparticularly, to a method for detecting whether vertical deviation of anoptical disc occurs while the optical disc is spinning in an opticaldisc player or an optical disc writer.

2. Description of the Prior Art

Vertical deviation refers to the wobbling of an optical disc, along theperpendicular direction of the spinning level that the optical disc isspinning on, while the optical disc is spinning in the optical discplayer or optical disc writer. Vertical deviation causes data reading tobe unstable, writing quality to be inconsistent, and noise to beproduced while the machine is operating.

Vertical deviation usually results from poor quality of the opticaldisc; this kind of undesired disc is called vertical deviation disc. Inthe field of disc manufacturing, there are many related technologies toprevent vertical deviation discs from being manufactured. Besides, manyindustrial instruments are used to detect whether an optical disc is avertical deviation disc.

However, consumers may encounter a vertical deviation disc while usingan optical disc player or optical disc writer. The reason could beattributed to inadequate quality management of the disc manufacturer orthe imbalanced mass of the optical disc caused by damage after theoptical disc left the factory. Because the prevention of verticaldeviation is considered to be the responsibility of the discmanufacturers, optical disc players or optical disc writers generallydon't include the detection method for detecting whether the opticaldisc is a vertical deviation disc.

Besides, an optical disc player or optical disc writer can read some ofthe vertical deviation discs. In the prior art, an optical disc playeror optical disc writer is designed to be able to keep the focus lengthfrom the optical disc in order to read data, the so-called focus.Therefore, although the vertical deviation disc wobbles along theperpendicular direction of the spinning level, the pickup head canfollow the wobbling of the optical disc and keep focusing to read data.

Because the prevention of vertical deviation of an optical disc isconsidered to be the responsibility of the disc manufacturers, andbecause some of the vertical deviation discs are still readable,manufacturers of optical disc player and optical disc writer usuallyignore the problem of vertical deviation. Users of optical disc playersand optical disc writers depend on the abnormal noise made while theoptical disc is spinning in the machine or on inconsistent quality ofreading or writing to determine whether the optical disc presently usedis a vertical deviation disc. Therefore, the conventional optical discplayer and optical disc writer lack a vertical deviation disc detectionmethod.

SUMMARY OF THE INVENTION

It is, therefore, a primary objective of the present invention toprovide a method of vertical deviation disc detection for optical discplayers or optical disc writers to solve the problems mentioned above.

According to the present invention, a method is provided for detectingwhether vertical deviation of an optical disc occurs while the opticaldisc is spinning in an optical disc player. The optical disc playercomprises a pickup head and a focus actuator. The pickup head ispredeterminedly installed in a balanced position at a focal distancefrom the optical disc for reading data on the optical disc and generatesa focus error signal. When the pickup head approaches and then movesaway from the balanced position, a S-curve appears in the focus errorsignal. The focus actuator actuates the pickup head according to aninput control signal, so that the pickup head is kept substantially atthe focal distance from the optical disc.

When the optical disc player has not yet successfully focused on theoptical disc, the waveform of the input control signal is designed toenable the actuator to actuate the pickup head back and forth repeatedlywithin a predetermined range. Consequently, the pickup head willgenerate the focus error signal that comprises a plurality of S-curves.A focus controller identifies the zero crossing points of S-curves inthe focus error signal, and obtains a plurality of input control valuesin the input control signal corresponding to the zero crossing points.In the method, the variation of the input control values is calculated,and whether vertical deviation of the optical disc has occurred isdetermined according to a predetermined vertical deviation judgmentprocedure.

The vertical deviation disc detection method according to the presentinvention can be employed in the system of an optical disc player oroptical disc writer to have the focus actuator actuate the pickup headrepeatedly within a predetermined range. This method also uses thevariation of the plurality of input control values in the input controlsignal corresponding to the zero-crossing points of the S-curves in thefocus error signal, thus determining whether vertical deviation hasoccurred. Alternatively, when an optical disc is focused, the presentinvention can use the variation of input control values to determinewhether vertical deviation occurs. Therefore, in the present invention,an optical disc player or optical disc writer can detect a verticaldeviation disc, and according to the method provided by the presentinvention, it restricts the maximum speed of writing or reading on avertical deviation disc to reduce the noise and to strengthen thestability of writing or reading.

It is an advantage of the present invention that the detection methodcan detect a vertical deviation disc. As a result, the user is informedwhether an optical disc is a vertical deviation disc, directly from theoptical disc player or optical disc writer.

These and other objectives of the present invention will no doubt becomeobvious to those skilled in the art after reading the following detaileddescription of the preferred embodiment, which is illustrated in variousfigures and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of an optical disc player, which isequipped with a vertical deviation disc detection method according tothe present invention.

FIG. 2 is the sketch of the waveforms of the focus error signal and theinput control signal in FIG. 1.

FIG. 3 is the sketch of the waveform of the focus error signal in FIG. 2superimposed with the waveform of the input control signal.

FIG. 4 is the flow chart of the vertical deviation disc detection methodaccording to the present invention.

FIG. 5 is the flow chart of another embodiment of vertical deviationdisc detection method according to the present invention.

FIG. 6 is the sketch of both the waveforms of the focus error signal andof the input control signal when the optical disc player is focusing ona normal disc.

FIG. 7 is the sketch of both the waveforms of the focus error signal andof the input control signal when the optical disc player is focusing ona vertical deviation disc.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Please refer to FIG. 1. FIG. 1 is a schematic diagram of an optical discplayer 10, which is equipped with a vertical deviation disc detectionmethod according to the present invention. The vertical deviation discdetection method, according to the present invention, is used to detectwhether optical deviation occurs while an optical disc 18 is spinning inthe optical disc player 10. The optical disc 18 comprises a data layerto record data thereon. The optical disc player 10 comprises a spinningmodule 12, a pickup head 14, and a control circuit 16. The spinningmodule 12 is used to spin the optical disc 18. The spinning module 12comprises a disc holder 11 to hold the optical disc 18 at a horizontallevel and a spindle motor 13 to spin the optical disc 18 around apredetermined center.

The optical head 14 is predeterminedly installed in a balanced positionat a focal distance from the optical disc 18 for reading data on theoptical disc 18 and then generating a focus error signal 34. When thepickup head 14 approaches and then moves away from the balancedposition, an s-shaped curve, known as S-curve, appears in the focuserror signal 34.

The pickup head 14 comprises a laser diode 20, a photo sensor 24, a RFamplifier 26, and a lens set 29. The laser diode 20 emits a readinglightbeam of a specific wavelength to read the data on the optical disc18. The photo sensor 24 receives the lightbeam reflected from theoptical disc 18 and then generates a set of RF signals. The RF amplifier26 performs signal amplification and signal processing on the RF signalsto generate the focus error signal 34. The lens set 29 assists thefocusing of the laser diode 20 and the photo sensor 24.

The lightbeam emitted from the laser diode 20 can be read by the photosensor 24 after the lightbeam being reflected by the optical disc 18.The photo sensor 24 can generate a set of RF signals according toseveral focus error detection methods such as knife-edge method,astigmatic method or light measuring method. The RF amplifier 26processes the set of RF signals and generates the focus error signal 34.

The control circuit 16 comprises a focus controller 28, a focus driver30 and the focus actuator 32. The focus controller 28 receives the focuserror signal 34. When the optical disc player 10 has not yetsuccessfully focused on the optical disc 18, the control circuit 16 isan open loop. The focus controller 28 can generate an input controlsignal 36 according to its operating needs. When the optical disc player10 focuses on the optical disc 18, the control circuit 16 becomes aclose-loop. According to the focus error signal 34 it receives, thefocus controller 28 will generate the input control signal 36 and sendto the focus driver 30.

According to the input control signal 36, the focus driver 30 generatesa driving current 38 to drive the focus actuator 32, which in turndrives the pickup head 14 correspondingly. The focus actuator 32actuates the pickup head 14 along a plane that is perpendicular to thespinning plane of the optical disc 18. Therefore, the focus actuator 32correspondingly actuates the pickup head 14 according to the inputcontrol signal 36; as a result, the pickup head 14 is kept substantiallyat the focal distance from the optical disc 18.

Please refer to FIG. 2 & FIG. 3. FIG. 2 is the sketch of the waveformsof both the focus error signal 34 and the input control signals 36 inFIG. 1. FIG. 3 is the sketch of the waveform of the focus error signal34 in FIG. 2 superimposed with the waveform of the input control signal36. With the focus error signal 34 and input control signals 36, thevertical deviation disc detection method of the present invention willbe explained in the following paragraphs. When the optical disc player10 is not yet focused on the optical disc 18, an input control signal36, that is designed to be a sawtooth waveform, is first transmitted tothe focus actuator 30 (FIG. 1). The input control signal 36 is the focusactuator input voltage that actuates the pickup head 14 back and forthrepeatedly in a predetermined range along a plane that is perpendicularto the spinning plane of the optical disc 18. The value of everysawtooth focus actuator input voltage is proportional to the distancebetween the pickup head 14 and the optical disc 18. The repeatedmovement of the pickup head 14 generates a focus error signal 34 thatcomprises a plurality of S-curves 40, and the zero crossing points 42 ofthe S-curves 40 occur when the distance between the pickup head 14 andthe optical disc 1 8 is the focal distance.

As shown in FIG. 3, the zero crossing points 42 of the S-curves 40 inthe focus error signals 34 are identified to calculate the input controlvalues 44 corresponding to the zero crossing points 42 on the inputcontrol signal 36. The input control values 44 are the input voltages ofthe focus actuator 32. The focus controller calculates the variation ofthose input control values 44 and determines whether the optical disc 18vertically deviates according to a predetermined vertical deviationjudgment procedure.

In the vertical deviation judgment procedure, the focus controller 28determines whether the optical disc 18 vertically deviates by performingsorting on the input control values 44, which correspond to the zerocrossing points 42, by using the difference between the maximum and theminimum of the input control values 44 to represent the variation of theinput control values 44, and by comparing the difference with apredetermined vertical deviation disc threshold.

When the optical disc 18 is determined to be a vertical deviation disc,the focus controller 28 then restricts the maximum speed of reading orwriting. For example, when the optical disc 18 is determined to be avertical deviation disc, the focusing controller 28 lowers down thespeed of reading from 48× to 32×. By lowering the speed, the noise isreduced, and the stability is strengthened while using a verticaldeviation disc by an optical disc player or writer.

As to the method to determine the vertical deviation disc threshold, theaforementioned detection method is performed in advance separately on atleast one tilted optical disc and on at least one normal optical disc toderive the corresponding variation between the two. The verticaldeviation disc threshold is then accordingly determined, based onstatistical principles and rule of thumb.

According to the present invention, the detection method of verticaldeviation disc uses the focus error signal 34 and the sawtooth designedinput control signal 36, so as to calculate the variation of thedisplacement of the pickup head 14 along the perpendicular directionwhen the distance between the pickup head 14 and the optical disc 18 isthe focal distance. And in the detection method, whether the verticaldeviation of the optical disc has occurred is determined according tothe variation. Comparing with the conventional optical disc player orwriter that depends on the user to determine whether vertical deviationof the optical disc occurs according to abnormal noises or to theinstability of data reading or data writing, the present invention cando the same thing with the optical disc player or optical disc writeritself through quantitative data. According to the present invention,the detection method can also restrict the maximum speed of reading orwriting to reduce the noise and to strengthen the stability of readingand writing.

Please refer to FIG. 4. FIG. 4 is the flow chart of the verticaldeviation disc detection method according the present invention. WithFIG. 1, the vertical deviation disc detection method according to thepresent invention comprises the following steps:

Step 100: Start.

Step 102: Activate the laser diode 20.

Step 104: Activate the spinning module 12.

Step 106: Enter the input control signal 36 that is designed to be asawtooth waveform to the focus actuator 30, so as to have the focusactuator 30 to actuate the pickup head 14 back and forth repeatedly in apredetermined range.

Step 108: Record the waveform of the focus error signal 34.

Step 110: Identify the zero crossing points 42 of the plural S-curves 40in the focus error signal 34, and calculate the input control values 44which correspond to the zero crossing points 42 in the input controlsignal 36. Sort those input control values 44. The difference betweenthe maximum and the minimum of the input control values 44 is used torepresent the variation of the input control values 44.

Step 112: Determine whether the variation is greater than the verticaldeviation disc threshold. If the answer is yes, go to step 114; if not,jump to step 116.

Step 114: Determine the optical disc 18 to be a vertical deviation disc.Stop.

Step 116: Determine the optical disc 18 to be a normal disc.

The vertical deviation disc threshold is determined by performing thesteps from 100 to 110 in FIG. 4 with many normal and vertical deviationdiscs separately to calculate the corresponding variation between normaland vertical deviation discs, and according to statistic principles andrule of thumb to determine the vertical deviation disc threshold.

Please refer to FIG. 5. FIG. 5 is the flow chart of another embodimentof vertical deviation disc detection method according to the presentinvention. Another embodiment according to the present invention isrelated to a vertical deviation disc detection method when the opticaldisc player 10 already focuses on the optical disc 18. This verticaldeviation disc detection method comprises the following steps:

Step 200: Start.

Step 202: Activate the laser diode 20.

Step 204: Activate the spinning module 12.

Step 206: Focus on the optical disc 18.

Step 208: Record the waveform of the input control signal 36.

Step 210: Record the variation of the amplitudes of input control signal36.

Step 212: Determine whether the variation is greater than the verticaldeviation disc threshold. If the answer is yes, go to the step 214; ifnot, jump directly to step 216.

Step 214: Determine the optical disc 18 to be a vertical deviation disc.Stop.

Step 216: Determine the optical disc 18 to be a normal disc.

Focus is a normally used technology on optical disc players or opticaldisc writers. The focus controller 28 determines whether the pickup head14 and the optical disc 18 are kept at the focal distance from eachother by the focus error signal 34. The focus controller 28 thengenerates an input control signal 36 to actuate the pickup head 14 so asto keep the pickup head 14 and the optical disc 18 at the focal distancefrom each other.

Please refer to FIG. 6 and FIG. 7. FIG. 6 is the sketch of both thewaveforms of the focus error signal 52 and the input control signal 54when the optical disc player is focusing on a normal disc. FIG. 7 is thesketch of both the waveforms of the focus error signal 56 and the inputcontrol signal 58 when the optical disc player is focusing on a verticaldeviation disc. From FIG. 6 and FIG. 7, it can be found that when theoptical disc is focused, the focus error signal 52 and 56 of a normaldisc and a vertical deviation disc, respectively, are substantially keptat a certain value. The input control signals 54 and 58 are the focusactuator input voltages of the focus actuator 30, and the signals canrepresent the function of displacement of the pickup head 14.

As shown in FIG. 7, when vertical deviation occurs, the focus actuator28 must generate an input control signal 58 with a greater variation soas to keep the pickup head 14 at the focal distance from the verticallywobbling optical disc 18. This embodiment uses such characteristic ofthe input control signals 58, when the optical disc 18 is focused, todetermine whether the optical disc 18 is a vertical deviation disc. In apractical operation, a filter can be employed to filter the highfrequency noise of the waveform of the input control signal 58.

Summing up the above-mentioned descriptions, in the vertical deviationdisc detection method according to the present invention, the opticaldisc player or optical disc writer repeatedly actuates the pickup headback and forth in a predetermined range, and thus, determines whethervertical deviation occurs with the variation of the plural input controlvalues in the input control signal; the input control values correspondto the zero crossing points of the S-curves in the focus error signal.Alternatively, when the optical disc is focused, the present inventionuses the variation of the input control values to determine whethervertical deviation of an optical disc occurs. Therefore, the presentinvention can allow the optical disc player or optical disc writer todetect a vertical deviation disc through a quantitative method and canrestrict the maximum speed of reading or writing according to theabove-mentioned method to reduce the noise and to strengthen thestability of reading or writing.

With the example and explanations above, the features and spirits of theinvention will be hopefully well described. Those skilled in the artwill readily observe that numerous modifications and alterations of thedevice may be made while retaining the teaching of the invention.Accordingly, the above disclosure should be construed as limited only bythe metes and bounds of the appended claims.

1. A detection method to detect, while an optical disc is spinning in anoptical disc player, whether vertical deviation of the optical discoccurs, the optical disc player comprising: a pickup headpredeterminedly positioned at a focal distance from the optical disc forgenerating a focus error signal having a plurality of S-curves therein;and a focus actuator configured to actuate the pickup head based ondirection from an input control signal, so that the pickup head is keptsubstantially at the focal distance from the optical disc; the verticaldeviation disc detection method comprising the following steps: beforethe optical disc player successfully focuses on the disc, designing awaveform of the input control signal to enable the actuator to actuatethe pickup head back and forth repeatedly within a predetermined range,and consequently to enable the pickup head to generate the focus errorsignal having plural S-curves; identifying a zero crossing point of theS-curve in the focus error signal and an intersecting point where theinput control signal intersects the S-curve; obtaining from the inputcontrol signal an input control value corresponding to the intersectingpoint and the zero crossing point; calculating the variation of aplurality of obtained input control values; and determining whethervertical deviation of the optical disc occurs based on the calculatedvariation of the input control values.
 2. The detection method of claim1, wherein the input control signal is a focus actuator input voltage,and the input control values are the corresponding input voltages. 3.The detection method of claim 2, wherein the input control signal isdesigned to be a sawtooth waveform so as to enable the focus actuator toactuate the pickup head back and forth repeatedly, and the value of theinput voltage of every section of the sawtooth waveform is proportionalto the distance between the pickup head and the optical disc.
 4. Avertical deviation disc detection method to detect whether verticaldeviation of an optical disc occurs while the optical disc is spinningin an optical disc player, the optical disc player comprising: a pickuphead predeterminedly installed in a balanced position at a focaldistance from the disc for reading data on the optical disc andgenerating a focus error signal, wherein when the pickup head approachesand then moves away from the balanced position, an S-curve appears inthe focus error signal; and a focus actuator, for actuating the pickuphead according to an input control signal, so that the pickup head iskept substantially at the focal distance from the optical disc; thevertical deviation disc detection method comprising the followingprocedures: when the optical disc player has not yet successfullyfocused on the disc, a waveform of the input control signal beingdesigned to enable the actuator to actuate the pickup head back andforth repeatedly within a predetermined range, and consequently toenable the pickup head to generate the focus error signal, having aplurality of S-curves; identifying zero crossing point of S-curves inthe focus error signal, and obtaining a plurality of input controlvalues in the input control signal corresponding to the zero crossingpoints; and calculating the variation of the input control values anddetermining whether vertical deviation of the optical disc occursaccording to a predetermined vertical deviation judgment procedure. 5.The detection method of claim 4, wherein the optical disc playercomprises a spinning module to spin the optical disc, the spinningmodule comprising: a disc holder to hold the optical disc at ahorizontal level; and a spindle motor to enable the optical disc to spinaround a predetermined center.
 6. The detection method of claim 4,wherein the pickup head comprises: a laser diode emitting a readinglightbeam of a specific wave length to read the data on the opticaldisc; a photo sensor for receiving the lightbeam reflected from theoptical disc and generating a set of RF signals; an RF amplifier forperforming signal amplification and signal processing on the RF signalsto generate the focus error signal; and a lens set for assisting thefocusing of the laser diode and the photo sensor.
 7. The detectionmethod of claim 6, wherein the optical disc player further comprises acontrol circuit that comprises a focusing controller, a focus driver andthe focus actuator.
 8. The detection method of claim 4, wherein theinput control signal is a focus actuator input voltage, and the inputcontrol values are the corresponding input voltages.
 9. The detectionmethod of claim 8, wherein the input control signal is designed to be asawtooth waveform so as to enable the focus actuator to actuate thepickup head back and forth repeatedly, and the value of the inputvoltage of every section of the sawtooth waveform is proportional to thedistance between the pickup head and the optical disc.
 10. The detectionmethod of claim 4, wherein after the vertical deviation of the opticaldisc is determined to occur, the vertical deviation judgment procedurerestricts the maximum speed of writing and reading of the optical disc.11. The detection method of claim 4, wherein the vertical deviationjudgment procedure determines whether the vertical deviation of theoptical disc occurs by practicing the following steps: performingsorting on the input control values which correspond to the zerocrossing points, using the difference between the maximum and theminimum of the input control values to represent the variation of theinput control values, and comparing the difference with a predeterminedvertical deviation disc threshold.
 12. The detection method of claim 11,when the vertical deviation disc threshold is to be determined, theaforementioned detection method is performed in advance on at least onetilt optical disc and on at least one normal optical disc to derive thecorresponding variation of both, and the vertical deviation discthreshold is accordingly determined, based on statistical principles andrule of thumb.
 13. A vertical deviation disc detection method to detectwhether vertical deviation of an optical disc occurs while the opticaldisc is spinning in an optical disc player, the optical disc playercomprising: a pickup head predeterminedly installed in a balanceposition at a focal distance from the optical disc for reading data onthe optical disc and generating a focus error signal; and a focusactuator for actuating the pickup head according to an input controlsignal, so that the pickup head is kept substantially at the focaldistance from the optical disc; the detection method comprising thefollowing steps: when the optical disc player successfully focuses onthe optical disc, recording the waveform of the input control signal andthe variation of the amplitudes, and comparing the variation of theamplitudes with a predetermined vertical deviation disc threshold todetermine whether the vertical deviation of an optical disc occurs. 14.The detection method of claim 13, wherein a filter is further employedto filter the high frequency noise in the input control signal.
 15. Thedetection method of claim 13, wherein the optical disc player comprisesa spinning module to spin the optical disc, the spinning modulecomprising: a disc holder to hold the optical disc at a horizontallevel; and a spindle motor to enable the optical disc to spin around apredetermined center.
 16. The detection method of claim 13, wherein thepickup head comprises: a laser diode emitting a reading lightbeam of aspecific wavelength to read the data on the optical disc; a photo sensorfor receiving the lightbeam reflected from the optical disc andgenerating a set of RF signals; an RF amplifier for performing signalamplification and signal processing on the RF signals to generate thefocus error signal; and a lens set for assisting the focusing of thelaser diode and the photo sensor.
 17. The detection method of claim 13,wherein the optical disc player further comprises a control circuitwhich comprises a focusing controller, a focus driver and the focusactuator; the focus controller generates the input control signal to thefocus actuator according to the received focus error signal, and thefocus driver also generates a driving current to drive the focusactuator so as to move the pickup head correspondingly.
 18. Thedetection method of claim 13, wherein the input control signal is afocus actuator input voltage for representing a function of displacementof the pickup head.
 19. The detection method of claim 13, wherein whenvertical deviation of the optical disc is judged to occur, the verticaldeviation judgment procedure restricts the maximum speed of writing andreading of the optical disc.